When \(\phi \)  is smooth and \(p\in \Gamma _\phi \) , we define the tangent plane to \(\Gamma _\phi \)  at \(p\)  to be the vertical plane \(P_p = p \langle X+\nabla _\phi \phi (p) Y, Z\rangle \)  with slope \(\nabla _\phi \phi (p)\) . For \(t>0\) , \(p s_t(p^{-1} \Gamma _\phi )\)  is the scaling of \(\Gamma _\phi \)  centered at \(p\) , and as \(t\rightarrow \infty \) , \(p s_t(p^{-1} \Gamma _\phi )\)  converges to \(P_p\) . More generally, when \(\phi \)  is intrinsic Lipschitz, a Rademacher-type theorem holds for almost every \(p\in \Gamma _\phi \) , so the definition of \(\nabla _\phi \phi (p)\)  can be extended so that \(p s_t(p^{-1} \Gamma _\phi )\)  converges to \(P_p\)  for almost every \(p\in \Gamma _\phi \)  [1]}.
